| Vegetation rehabilitation is the fundamental measure to control soil erosion in the Loess Plateau.Understanding the benefit of sediment and runoff reducing in different vegetation structure is the key to study the mechanism of water and soil conservation in this region.The objective of this study was to research the mechanism of the runoff and sediment yield in different shrub-grass vegetation coverage and rainfall intensity,implement different shrub-grass structure at the different slope,rainfall intensity to analyze the variation process of sediment and runoff and quantitative the relationship between vegetation cover.In order to provide good references on ecological environment and vegetation construction in the Loess Plateau,this paper summaried the impact on Ecological Environment and the existing problems since the Grain for Green Project launched in the Loess Plateau.The results are as follows:(1)The initial runoff yielding time increases with the increased of vegetation coverage and the decreased slope.The flow velocity decreases with the increased of vegetation coverage and the decreased slope.The initial runoff yielding time was 70%>66%>60%>.42%>35%>26%>18%>bare land under the same rainfall intensity and slope.It?s conclude that runoff time has significantly positive correlation with vegetation coverage and negative correlation with the slope by the regression relation,that is,the initial time of runoff is getting shorter as the steeper slope under the same rainfall intensity and vegetation coverage.Under the same rainfall intensity and slope,the vegetation coverage has negative correlation with the influence of slope flow velocity,namely,the larger the vegetation coverage,the smaller the velocity of the slope surface.(2)The runoff intensity and erosion rate decreased with the increase of vegetation coverage,and the infiltration rate increased with the increase of vegetation coverage.Under the two types of rainfall,the change order of runoff intensity and erosion rate of different vegetation coverage was 35%>42%>60%>70%,18%>26%>43%>66%.The infiltration rate is in reverse order.The runoff intensity of each simulated rainfall starts to increase sharply and then increased slowly to the stable state of change,which showed the change trend of power function.in the high rainfall intensity,erosion rate increased dramatically at first,then slow down to a steady state erosion rate fluctuation change trend.In the same rainfall intensity and slope,erosion rate greatly reduced with the increaseing of vegetation coverage;the infiltration rate droped firstly and then slows down to a stable state.(3)The amount of runoff and sediment yield of simulated rainfall increased significantly with the increase of vegetation coverage,and the vegetation coverage played a major role in reducing sediment and streamflow,and the shrub coverage was second.Bringing carried out a statistical analysis on the vegetation coverage,shurb,grass vegetation coverage has a significant influence on amount of runoff and sediment yield,and grass coverage plays a leading role,while the interaction of the vegetation don't affected,was not significant.By regression analysis,the relationship between the total sediment yield and runoff concertration and vegetation coverage can be obtained by using the binomial function,y=ax~2+bx+c(where y represents the total amount of sediment yield;X represents vegetation coverage;a,b,c are the equation coefficient),analyzed in the low-intensity rainfall(1.0 mm/min)and the vegetation coverage on the range of 73.56%~87.68%,the total amount of runoff and sediment yield,and high rainfall intensity(2.5 mm/min)under the critical coverage of 61.09%~78.88%.(4)The vegetation restoration,the rational utilization of land resources and the climate improvement of the area have been remarkable since the Grain for Green Project has been implemented in the Loess Plateau.But there?re some problems in vegetation structure configuration,bearing capacity of water resources,cultivated land and grain production problems.It?s necessary to adjust measures to local conditions,deploy rationally vegetation structure,strengthen the effective utilization of land resources and the follow-up management,in order to further develop the ecological and economic benefits of the Grain for Green Project. |
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